Gas turbines customarily have a rotatably mounted rotor which is enclosed by a fixed housing. The stationary sub-assemblies of the gas turbine are collectively also referred to as a stator. A flow passage, which extends in the axial direction, for a compressible flow medium is arranged between the rotor and the stator. Rotor blades, which project into the flow passage and are grouped together, forming blade rows, are customarily fastened on the rotor. The rotor blades on the compressor side serve for compressing a medium and on the turbine side serve for driving the rotor shaft by means of impulse transfer from a hot pressurized flow medium.
The rotating component of a gas turbine, which is also referred to as a rotor, for service-related reasons is customarily subjected to a high mechanical and thermal stress. In particular, the rotor components are heavily stressed as a result of the high temperature of the operating medium and as a result of the forces which act upon the rotor during operation of the gas turbine. In order to nevertheless be able to ensure the operational safety on the one hand and to keep the production costs of the rotor within acceptable limits on the other hand, a number of constructional possibilities for such turbine rotors were proposed in the past.
One of these constructional possibilities makes provision for also assembling the rotor of stationary gas turbines from individual rotor components, wherein the individual rotor components are held together via a tie-bolt. For this purpose, each rotor component has an axially extending recess through which the tensioned tie-bolt can extend. By means of threaded nuts which are screwed onto the tie-bolt at the end, this can be tensioned, as a result of which the rotor components, which abut against each other by their end faces, can be clamped to each other. The rotor components are then pressed against each other by the tie-bolt and transmit the rotational forces which act upon them via a so-called Hirth toothing which, disposed on the end face in each case, forms a form-fit between two abutting rotor components.
The rotor of the gas turbine is arranged in the housing of the turbine by means of suitable bearings at the ends. Instead of the threaded nuts, on the casing side more complexly designed components can also be screwed onto the end of the tie-bolt, which in addition to clamping the rotor components also enable further functions, such as the supporting of the rotor in a radial bearing and/or thrust nearing.
During operation of the gas turbine, however, vibrations occur in the rotor, the frequency of which inter alfa is dependent upon the spacing of the two thrust bearings, i.e. upon the freely vibrating length of the rotor and especially upon the freely vibrating length of the tie-bolt, in the case of such a type of construction. With increasing overall length of the gas turbine, the freely vibrating length of the tie-bolt also increases, which leads to its natural frequency being shifted to a lower level close to the rotational frequency.